http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-828

I haven't decided which tweeter to use yet. Any help or advice are appreciated.

Gavin

To have an array, the system has to be coupled with the floor and the ceiling, and you have to be in the nearfield for listening. The nearfield is roughly 3 times the array size, which means that you would have to listen to the system less than 4 feet from the speakers, and the size doesn't couple with the floor and the ceiling. And even at this distance you would not be in the nearfield for the tweeter. So you are just building a large point source speaker system. I suggest you consider a D'Appolito MTM design with a couple of larger woofers at the bottom.

There is no such thing as a small array. You either have a line array or you don't.

Marlboro

That might be the worst definition of an array I've ever seen written. No, an array doesn't have to be coupled with anything to be an array, and your listening position has nothing whatsoever to do with what constitutes an array. If you'd like, I'll send you a copy of Griffin's white paper so you can brush up.

The array described in the report is one that is two way with a woofer system that goes down to a bit below 100hz, and a tweeter system above roughly 1600 to 3000hz, thus a two way system. Usually a low frequency driver is used to complement the array. Thus, Dr. Griffin goes on to describe the required height of both the woofer and the tweeter array portions on page 10.

Woofer and Tweeter line height is described specifically.
First woofer line height:

PAGE 10: ".......Finally, best low frequency coupling to the boundaries occurs wherein the distances between either end of the line and the ceiling and floor are less than a wavelength, respectively. Typically, the woofer line length height needs to be greater than 70% of the room height for effective boundary coupling."

Tweeter line height:

"....Tweeter Line Height. As for the woofer line length, the ideal tweeter line length would also extend from near the floor to the ceiling. Such a length would assure near field sound radiation for the entire room. Possible implementations would be a very long ribbon/planar tweeter or a large number of small dome tweeters if a floor to ceiling line length is desired. However, either of these implementations would be expensive."

Because of the expense, three options are considered.

Part of the second is here: "....Listening Position Coverage. Consider also the listening position and whether you desire to cover the sitting position (slightly less than one meter (39.4”) above the floor at ear level) only or both standing (typically up to 1.8 m (70.9”) height) and sitting positions. Hence, for many situations a tweeter line height would need to be grater than one meter to adequately cover both sitting and standing positions."

Both the line height considered here in Jim's paper and the discussion regarding the nearfield make it clear to most readers that there is a requirement for nearfield listening and line height itself to consider that the speaker system is a line array.

Anything that does not meet these criteria is not part of the description that the Griffin report describes in its title:

"Design Guidelines for Practical Near Field Line Arrays"

It may be a mini line array, but its not a nearfield line array which provides all the benefits described in a line array.

Sorry.....

Marlboro

That isn't what you said, is it? Lesson you should learn: if you're going to be an arrogant know-it-all, make sure you know it all.

None of the rest of use do much more than quote it. The bottom line is that if one is building a line array for an inside dwelling, and one wants all the benefits of it with low distortions and wide sound stage, one is constrained to use those parameters which require a large line that goes 70% of floor to ceiling in the mid/base area, and at least one meter in the tweeter.

Everything else is design compromise.

If Ivor feels compelled to provide flame bait when he's not sure what the poster is saying, rather than ask a question, then that is his prerogative. I stand by my statement that an array that has four speakers in it is not a line array.

I'm sorry if Ivor misunderstood what I was saying. I often suffer from imprecise speech when it comes to these things as I lack a technical background, or an EE degree. Its a hazard. But having built one of these bad boys to Jim's specifications, I assure you that I understand what his white paper says.

Kind regards,

Marlboro